U.S. patent application number 17/158671 was filed with the patent office on 2021-05-20 for self-interference digital holographic system.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The applicant listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Ki Hong CHOI, Sung Wook MIN, Jun Kyu YIM.
Application Number | 20210149338 17/158671 |
Document ID | / |
Family ID | 1000005360874 |
Filed Date | 2021-05-20 |
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United States Patent
Application |
20210149338 |
Kind Code |
A1 |
MIN; Sung Wook ; et
al. |
May 20, 2021 |
SELF-INTERFERENCE DIGITAL HOLOGRAPHIC SYSTEM
Abstract
A self-interference digital holographic system obtains
interference patterns of incident light using a simple geometric
phase lens, and obtains a holographic image of a target object
using the interference patterns. The self-interference digital
holographic is fabricated simply in a low cost and in a
miniaturized size, and the use thereof as actual products is
extended to a wide range of applications. The phase of incident
light is be changed by rotating a polarizer, independently of a
change in the optical path. Phase-shifting effects are obtained
with fewer errors in all wavelength ranges, and a more accurate
holographic image is produced. A single birefringence hologram is
obtained by a one-time image-capturing process by simultaneously
forming interference patterns from phase-shifted linearly-polarized
beams by space division, using a phase shifter on the basis of
space division. Moving holographic images can be captured.
Inventors: |
MIN; Sung Wook; (Seoul,
KR) ; CHOI; Ki Hong; (Seoul, KR) ; YIM; Jun
Kyu; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
|
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
1000005360874 |
Appl. No.: |
17/158671 |
Filed: |
January 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16233081 |
Dec 26, 2018 |
10921752 |
|
|
17158671 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03H 1/0443 20130101;
G03H 1/041 20130101; G03H 2223/22 20130101; G03H 2225/32
20130101 |
International
Class: |
G03H 1/04 20060101
G03H001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2018 |
KR |
10-2018-0011591 |
Feb 20, 2018 |
KR |
10-2018-0019865 |
Claims
1. A self-interference digital holographic system comprising: a
phase shifter configured to change incident light to
linearly-polarized light and sequentially vary a polarization
direction of the linearly-polarized light by an angle of
45.degree.; a geometric phase lens configured to change the
linearly-polarized light to left-circularly-polarized light and
right-circularly-polarized light; and an image sensor configured to
obtain an interference pattern formed from the
left-circularly-polarized light and the right-circularly-polarized
light.
2. The self-interference digital holographic system according to
claim 1, wherein the interference patterns formed from the
left-circularly-polarized light and the right-circularly-polarized
light of the incident light, the phase of which is sequentially
changed by the phase shifter, are sequentially obtained and are
combined, thereby producing a single birefringence hologram.
3. The self-interference digital holographic system according to
claim 2, wherein the phase shifter comprises: a rotatable polarizer
disposed in front of and concentrically with the geometric phase
lens such that the incident light enters the geometric phase lens
through the rotatable polarizer, the rotatable polarizer changing
the incident light to linearly-polarized light; and a polarizer
driver rotating the rotatable polarizer about a central axis.
4. The self-interference digital holographic system according to
claim 3, wherein the polarizer driver sequentially rotates the
rotatable polarizer by an angle of 45.degree..
5. The self-interference digital holographic system according to
claim 4, wherein the interference patterns formed from the
left-circularly-polarized light and the right-circularly-polarized
light produced from four beams of the incident light that have been
sequentially phase-changed by the phase shifter are sequentially
obtained and are combined, thereby obtaining a single birefringence
holographic image.
6. A self-interference digital holographic system comprising: a
polarizer configured to change incident light to linearly-polarized
light; a geometric phase lens configured to change the
linearly-polarized light to left-circularly-polarized light and
right-circularly-polarized light; a polarizer array comprised of a
plurality of polarizers having different types of light
transmission axis angles, wherein each of the plurality of
polarizers change the left-circularly-polarized light and
right-circularly-polarized light to two linearly-polarized beams;
and an image sensor configured to obtain interference patterns
formed from the two linearly-polarized beams.
7. The self-interference digital holographic system according to
claim 6, wherein each of the types of light transmission axis
angles of the plurality of polarizers has one of four different
types, which sequentially vary by 45.degree..
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S.
application Ser. No. 16/233,081 filed Dec. 26, 2018, which claims
priority to Korean Patent Application Number 10-2018-0011591 filed
on Jan. 30, 2018, and Korean Patent Application Number
10-2018-0019865 filed on Feb. 20, 2018, the entire contents of
which are incorporated herein for all purposes by this
reference.
BACKGROUND
Field
[0002] The present disclosure relates to a self-interference
digital holographic system. More particularly, the present
disclosure relates to a self-interference digital holographic
system that can obtain interference patterns of incident light
using a geometric phase lens, which is a simple optical component,
and obtain a holographic image of a target object using the
interference patterns, so that the self-interference digital
holographic system can be simply fabricated in a low cost and in a
miniaturized size, and the use thereof as actual products can be
extended to a wide range of applications. The self-interference
digital holographic system can be provided as an economically
inexpensive and complete transmission system, in which the phase of
incident light can be changed by rotating a polarizer, which is a
simple optical component. The phase change can be performed by
geometric phase shifting through the rotation of the polarizer,
instead of dynamic phase shifting in which an optical path is
directly changed. Since phase shifting is independent of a change
in the optical path, it is possible to obtain phase-shifting
effects having fewer errors in all wavelength ranges, and a more
accurate holographic image can be produced. In addition, the
self-interference digital holographic system can obtain a single
birefringence hologram by a one-time image-capturing process by
simultaneously forming interference patterns from phase-shifted
linearly-polarized beams by space division, instead of sequentially
obtaining the phase-shifted interference patterns, since a phase
shifter for removing noise is applied on the basis of space
division. Since a plurality of interference patterns can be
simultaneously obtained by a one-time image-capturing process, it
is possible to capture a holographic image of an object moving over
time, such as a living thing, as well as an image of a still
object, and it is possible to capture moving holographic
images.
DESCRIPTION
[0003] Recently, three-dimensional (3D) imaging technology has been
predicted to have significant effects in providing added value. For
example, it has been predicted that 3D imaging technology will be
widely used in almost all commercial and industrial fields, having
applications in areas such as filmmaking, broadcasting,
entertainment, as well as in the aerospace, military, and medical
areas. Recently, 3D imaging technology has not only been discussed
in terms of 3D image development communities, but is also emerging
as a national issue, in relation to future research and
development.
[0004] 3D imaging technology is generally categorized as either a
3D imaging technique using glasses, or as a glasses-free 3D imaging
technique, in which different images are provided to the eyes of a
viewer, thereby creating the perception of depth based on parallax.
The 3D imaging technique using glasses may further be categorized
as either 3D imaging using polarizing glasses, or 3D imaging using
shutter glasses. The glasses-free 3D imaging technique may further
be categorized as one of integral imaging based on parallax (e.g.
utilizing lenticular arrays, a parallax barrier, and parallax
illumination), in which different images are provided to the eyes
of a viewer as in the 3D imaging technique using glasses;
volumetric 3D imaging, in which cross-sectional images of an object
are continuously reproduced to actually generate a 3D image in
space; and holography, in which information regarding wave surfaces
of a 3D object are recorded and reproduced.
[0005] The 3D imaging technique based on binocular parallax, or
stereoscopic technique, has fundamental problems, such as headaches
or dizziness caused to human viewers, due to several reasons. These
problems may be caused by insufficient consideration of image
alignment, optical distortion, camera setting for adjustment of 3D
sensation, and emotional factors during 3D image production, as
well as the setting of a display device, flickering caused by
alternate scanning of right and left images, 3D image distortion
due to excessive negative depth, and the like.
[0006] Holography is a technique able to fundamentally overcome
such issues involved in viewing stereoscopic 3D images, which are
problems of 3D imaging technique based on binocular parallax. In
general, viewers perceive a 3D object on the basis of light
reflected from the object. When reflections of light from an object
can be generated, it may be possible to form an actual object
shape. A hologram is produced by illuminating such an object shape.
An object wave, produced by reflecting a laser beam from an object,
is combined with a laser beam incoming from another direction, and
the combined beams are recorded on photographic film. When the
beams incoming from different directions are combined, phase
differences between object waves reflected from respective points
of the object form an interference pattern. In the interference
pattern, both the amplitude and phase of the object are recorded.
The above-described object shape, recorded on photographic film in
the form of an interference pattern, is referred to as a hologram.
That is, a hologram is a 3D image recorded on a surface similar to
that of photographic film using an optical interference effect
created by two combined laser beams.
[0007] Holography records information regarding the amplitude and
phase of light propagated from an object, unlike in typical
photography, in which only intensity information of light is
recorded. Since to date there have been no sensors able to directly
record amplitude and phase information of visible light, such
amplitude and phase information of visible light is indirectly
obtained by an optical interference phenomenon. Although inference
is a phenomenon created by the interaction of light waves of an
object beam and a reference beam, it is difficult to obtain an
interference pattern without the use of laser light, the amplitude
and phase of which are artificially aligned. Accordingly, laser
light has mainly been used in holography to date.
[0008] However, when laser light is used, all light, except for
laser light, must be excluded. Thus, it is substantially impossible
to record a hologram outdoors. In order to overcome such a real
world problem, a self-interference holography technique has been
developed.
[0009] Self-interference holography obtains an interference pattern
by self-referencing, in which incident light, emitted or reflected
from an object, is divided, depending on the spatial or
polarization state. The divided light waves may propagate, after
being modulated to wave surfaces having different curvatures under
the influence of an interferometer or a polarization modulator, and
form an interference pattern on an image sensor. In this case,
self-interference holography is free of conditions on the light
source, since the interference is performed by twin light waves
produced from light emitted at the same time and in the same space.
Accordingly, an image can be captured using any type of light, such
as fluorescent light, incandescent light, LED light, or natural
light.
[0010] Although the concept of such a self-interference holography
technique is established, no systems in which self-interference
holography has actually been realized have been substantially
developed. In addition, a complex optical system must be used to
form an interference pattern by splitting incident light.
Accordingly, self-interference holography has not been applied to
actual products.
[0011] A holography technique in which optical components are
aligned along a single axis has advantages, in that the resolution
and area of an image sensor can be directly used for a hologram.
However, according to the interference formula, information
regarding a light source and twin-image information of an object
may be disadvantageously recorded, in addition to hologram
information of the object. In order to remove the light source
information and the twin image information from the obtained
hologram information, phase shifting may be used. When an optical
path of an object beam or a reference beam is finely adjusted to
have a length shorter than the wavelength in two to four stages,
phase information is finely varied. When intensity information of
light is measured at each stage and the measured intensity
information is then computed, a birefringence hologram, from which
the light source information and the twin image information are
removed, can be produced. In a four-stage phase shifting system, a
birefringence hologram is produced, as in Formula 1:
.0. ( x , y ) = tan - 1 I ( x , y ; 3 .pi. 2 ) - I ( x , y ; .pi. 2
) I ( x , y ; ( ) ) I ( x , y ; .pi. ) , ( 1 ) ##EQU00001##
[0012] where (x, y) is coordinates of an image sensor surface, I is
each phase-shifted image, and .PHI. is a birefringence
hologram.
[0013] In the holograph technique, a variety of phase-shifting
systems have been attempted for phase shifting. For example, in
such attempts, a set of equipment, such as a piezoelectric
actuator, which can finely move a mirror of an interferometer on
the nanometer scale, may be used, in addition to a spatial light
modulator capable of phase modulation. However, such equipment is
highly expensive and may be sensitive to external environmental
factors, such as temperature, moisture, and vibrations, which are
problematic. In addition, since the optical path is directly
modulated, sufficient phase modulation from 0.degree. to
360.degree. is possible only in a specific wavelength. The farther
away from the specific wavelength, the greater the phase shift
error may be, which is problematic.
[0014] Such a phase-shifting system may be applied in a manner of
sequentially changing the phase of light. Since the above-described
four-stage phase-shifting system can only produce a single
birefringence hologram by combining four pieces of phase-shifted
information in the four stages, a phase shifting time corresponding
to the four stages is required to produce a single birefringence
hologram. Accordingly, a hologram of a still object can be
produced, but a hologram cannot be produced from a moving object.
That is, it is impossible to capture moving holographic images,
which is fundamentally problematic.
[0015] The information disclosed in the Background section is
provided only to allow for a better understanding of the background
and should not be taken as an acknowledgment or any form of
suggestion that this information forms prior art that would already
be known to a person skilled in the art.
BRIEF SUMMARY
[0016] Various aspects of the present disclosure provide a
self-interference digital holographic system that can obtain
interference patterns of incident light using a geometric phase
lens, which is a simple optical component, and obtain a holographic
image of a target object using the interference patterns. The
self-interference digital holographic system can be simply
fabricated in a low cost and in a miniaturized size, and the use
thereof as actual products can be extended to a wide range of
applications.
[0017] Also provided is a self-interference digital holographic
system that can be provided as an economically inexpensive and
complete transmission system, in which the phase of incident light
can be changed by rotating a polarizer, which is a simple optical
component, without the use of complicated optical equipment or the
like. In addition, the phase change can be performed by geometric
phase shifting through the rotation of the polarizer, instead of
dynamic phase shifting in which an optical path is directly
changed. Since phase shifting is independent of a change in the
optical path, it is possible to obtain phase-shifting effects
having fewer errors in all wavelength ranges. Accordingly, a more
accurate holographic image can be produced.
[0018] Also provided is a self-interference digital holographic
system that can obtain a single birefringence hologram by a
one-time image-capturing process by simultaneously forming
interference patterns from phase-shifted linearly-polarized beams
by space division, instead of sequentially obtaining the
phase-shifted interference patterns, since a phase shifter for
removing noise is applied on the basis of space division. Since a
plurality of interference patterns can be simultaneously obtained
by a one-time image-capturing process, it is possible to capture a
holographic image of an object moving over time, such as a living
thing, as well as an image of a still object. Accordingly, it is
possible to capture moving holographic images.
[0019] According to an aspect, a self-interference digital
holographic system may include: a geometric phase lens disposed
such that incident light propagating from a target object passes
therethrough to change the incident light to
left-circularly-polarized light and right-circularly-polarized
light; and an image sensor receiving the left-circularly-polarized
light and the right-circularly-polarized light changed by the
geometric phase lens. An interference pattern is formed in a
self-interference manner by interference of the
left-circularly-polarized light and the right-circularly-polarized
light, changed from the incident light by the geometric phase lens,
and is obtained by the image sensor.
[0020] The self-interference digital holographic system may further
include a phase shifter disposed in front of the geometric phase
lens to change a phase of the incident light entering the geometric
phase lens.
[0021] The interference patterns formed from the
left-circularly-polarized light and the right-circularly-polarized
light of the incident light, the phase of which is sequentially
changed by the phase shifter, may be sequentially obtained and be
combined, thereby producing a single birefringence hologram.
[0022] The phase shifter may include: a rotatable polarizer
disposed in front of and concentrically with the geometric phase
lens such that the incident light enters the geometric phase lens
the rotatable polarizer, the rotatable polarizer changing the
incident light to linearly-polarized light; and a polarizer driver
rotating the rotatable polarizer about a central axis.
[0023] The polarizer driver may sequentially rotate the rotatable
polarizer by an angle of 45.degree..
[0024] The interference patterns formed from the
left-circularly-polarized light and the right-circularly-polarized
light produced from four beams of the incident light that have been
sequentially phase-changed by the phase shifter may be sequentially
obtained and be combined, thereby obtaining a single birefringence
holographic image.
[0025] The self-interference digital holographic system may further
include a fixed polarizer disposed between the geometric phase lens
and the image sensor such that the left-circularly-polarized light
and the right-circularly-polarized light pass therethrough, the
fixed polarizer changing the left-circularly-polarized light and
the right-circularly-polarized light to linearly-polarized
light.
[0026] The self-interference digital holographic system may further
include an incident lens disposed in front of the phase shifter to
condense the incident light propagating from the target object, so
that the incident light enters the geometric phase lens through the
phase shifter.
[0027] The self-interference digital holographic system may further
include a floating lens disposed between the geometric phase lens
and the fixed polarizer such that the left-circularly-polarized
light and the right-circularly-polarized light, changed by the
geometric phase lens, pass therethrough, thereby extending optical
paths of the left-circularly-polarized light and the
right-circularly-polarized light.
[0028] The self-interference digital holographic system may further
include a space division phase shifter disposed in front of the
image sensor such that the left-circularly-polarized light and the
right-circularly-polarized light, changed by the geometric phase
lens, are changed to two linearly-polarized beams before entering
the image sensor. The image sensor may have a light receiving area
included of a plurality of divided sections, and the space division
phase shifter causes the linearly-polarized beams entering the
image sensor have different phases according to the plurality of
divided sections. The image sensor simultaneously may obtain
interference patterns formed by the two linearly-polarized beams in
the plurality of divided sections, and a single birefringence
hologram may be obtained by combining the interference
patterns.
[0029] The space division phase shifter may include a
micro-polarizer array comprised of a plurality of micro-polarizers
changing transmission light to linearly-polarized beams, the
plurality of micro-polarizers being arranged to correspond to the
plurality of divided sections of the image sensor.
[0030] The plurality of divided sections of the image sensor may be
provided to correspond to a plurality of pixels of the image
sensor.
[0031] The plurality of micro-polarizers may have light
transmission axes at different angles, such that the
linearly-polarized beams that have passed through the
micro-polarizers have different phases.
[0032] Each of the light transmission axes of the plurality of
micro-polarizers may have one of four different types of light
transmission axis angles, which sequentially vary by
45.degree..
[0033] The plurality of micro-polarizers having the different types
of light transmission axis angles may be provided such that same
number of micro-polarizers, among the plurality of
micro-polarizers, are provided for each type of the different types
of light transmission axis angle.
[0034] The self-interference digital holographic system may further
include a fixed polarizer disposed in front of the geometric phase
lens such that the incident light enters the geometric phase lens
therethrough, the fixed polarizer changing the incident light to
linearly-polarized light.
[0035] The self-interference digital holographic system may further
include an incident lens disposed in front of the fixed polarizer
to condense the incident light propagating from the target object,
so that the incident light enters the geometric phase lens through
the fixed polarizer.
[0036] The self-interference digital holographic system may further
include a floating lens disposed between the geometric phase lens
and the space division phase shifter such that the
left-circularly-polarized light and the right-circularly-polarized
light, changed by the geometric phase lens, pass therethrough,
thereby extending optical paths of the left-circularly-polarized
light and the right-circularly-polarized light.
[0037] According to the present disclosure, it is possible to
obtain interference patterns of incident light using the geometric
phase lens, which is a simple optical component, and obtain a
holographic image of a target object using the interference
patterns. The self-interference digital holographic system can be
simply fabricated in a low cost and in a miniaturized size, the use
thereof as actual products can be extended to a wide range of
applications.
[0038] In addition, since the phase of incident light can be
changed by rotating the polarizer, which is a simple optical
component, without the use of complicated optical equipment or the
like, an economically inexpensive and complete transmission system
can be provided. In addition, the phase change can be performed by
geometric phase shifting through the rotation of the polarizer,
instead of dynamic phase shifting in which an optical path is
directly changed. Since phase shifting is independent of a change
in the optical path, it is possible to obtain phase-shifting
effects having fewer errors in all wavelength ranges. Accordingly,
a more accurate holographic image can be produced.
[0039] Furthermore, it is possible to change
left-circularly-polarized light and right-circularly-polarized
light, changed by the geometric phase lens, to linearly-polarized
light using the fixed polarizer, so that the linearly-polarized
light enters the image sensor. Since the interference between the
left-circularly-polarized light and the right-circularly-polarized
light can be further enhanced, clearer interference patterns can be
produced and a clearer holographic image can be obtained.
[0040] In addition, since the phase shifter for removing noise is
applied on the basis of space division, a single birefringence
hologram can be obtained by a one-time image-capturing process by
simultaneously forming interference patterns from phase-shifted
linearly-polarized beams by space division, instead of sequentially
obtaining the phase-shifted interference patterns. Since a
plurality of interference patterns can be simultaneously obtained
by a one-time image-capturing process, it is possible to capture a
holographic image of an object moving over time, such as a living
thing, as well as an image of a still object. Accordingly, it is
possible to capture moving holographic images.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] The above and other objects, features and advantages of the
present disclosure will be more clearly understood from the
following detailed description when taken in conjunction with the
accompanying drawings, in which:
[0042] FIG. 1 is a conceptual view illustrating a basic
configuration of a self-interference digital holographic system
according to exemplary embodiments;
[0043] FIGS. 2A, 2B, and 2C are conceptual views illustrating
characteristics of a geometric phase lens according to an exemplary
embodiment;
[0044] FIG. 3 is a conceptual view illustrating a configuration of
a self-interference digital holographic system to which a phase
shifter according to an exemplary embodiment is applied;
[0045] FIGS. 4 to 6 are perspective views illustrating a variety of
configurations of the self-interference digital holographic system
according to an exemplary embodiment;
[0046] FIG. 7 is a conceptual view illustrating a configuration of
a self-interference digital holographic system to which a space
division phase shifter according to another exemplary embodiment is
applied; and
[0047] FIG. 8 is a perspective view illustrating a specific
configuration of the self-interference digital holographic system
according to another embodiment.
DETAILED DESCRIPTION
[0048] Hereinafter, exemplary embodiments of the invention will be
described in detail with reference to the accompanying drawings.
Wherever possible, the same reference numerals will be used
throughout the drawings and the description to refer to the same or
like parts. In the following description, it is to be noted that,
when the functions of conventional elements and the detailed
description of elements related to the present disclosure may
render the gist of the present invention unclear, a detailed
description of those elements will be omitted.
[0049] FIG. 1 is a conceptual view illustrating a basic
configuration of a self-interference digital holographic system
according to exemplary embodiments, FIGS. 2A, 2B, and 2C are
conceptual views illustrating characteristics of a geometric phase
lens according to an exemplary embodiment, and FIG. 3 is a
conceptual view illustrating a configuration of a self-interference
digital holographic system to which a phase shifter according to an
exemplary embodiment is applied.
[0050] The self-interference digital holographic system according
to exemplary embodiments is configured to form an interference
pattern from incident light incoming from a target object by
self-interference. The self-interference digital holographic system
includes: a geometric phase lens 100 disposed such that incident
light passes therethrough to change the incident light to
left-circularly-polarized light and right-circularly-polarized
light; and an image sensor 200 receiving the
left-circularly-polarized light and the right-circularly-polarized
light split by the geometric phase lens 100.
[0051] The incident light is changed to the
left-circularly-polarized light and the right-circularly-polarized
light while passing through the geometric phase lens 100, and an
interference pattern is formed by interference between the
left-circularly-polarized light and the right-circularly-polarized
light. The interference pattern is formed on the image sensor 200
to be obtained by the image sensor 200.
[0052] More specifically, the geometric phase lens 100 is a device
functioning as a lens, based on a predetermined fixed alignment of
liquid crystal. A typical lens converges or diverges incident light
by modulation the wave surface of the incident light by adjusting
the thicknesses of media having different refractive indices
(dynamic phase modulation). In contrast, the geometric phase lens
causes a phase change by a change in the polarization state of
light on the basis of the birefringence of liquid crystal, thereby
modulating the wave surface of incident light. Since holographic
photography is used when manufacturing the geometric phase lens,
twin images of a lens surface are recorded. Accordingly, the
geometric phase lens exhibits a lens characteristic having both
negative and positive focal lengths.
[0053] Since liquid crystal is permanently aligned according to an
alignment film formed by curing of a photosensitive polymer,
instead of being electrically moved, the geometric phase lens may
function as an independent passive optical device. The geometric
phase lens is highly transparent, thin, and simple to manufacture,
which are advantageous.
[0054] In addition, due to polarization selectivity, when incident
light is right-circularly-polarized light, the incident light
converges depending on the focal length while being changed to
left-circularly-polarized light. When incident light is
left-circularly-polarized light, the incident light diverges
depending on the focal length while being changed to
right-circularly-polarized light. When linearly polarized light or
non-polarized light is incident, the incident light is split into
converging light and diverging light, with the energy of the
incident light being bisected. Here, the converging light is
left-circularly-polarized light, while the diverging light is
right-circularly-polarized light.
[0055] For reference, circular polarization means that the
direction of vibrations of electric displacement vector (or
magnetic field displacement vector) of a light wave circularly
rotates. When linearly polarized light is incident with a vibration
surface inclined at an angle of 45.degree. with respect to a main
axis of a quarter wave plate, light that has passed through the
quarter wave plate is circularly polarized light. Right circular
polarization refers to circular polarization in which an electric
vector of light rotates in a clockwise direction, from the
viewpoint of a viewer, while left circular polarization refers to
circular polarization in which an electric vector of light rotates
in a counterclockwise direction, from the viewpoint of a
viewer.
[0056] When right-circularly-polarized light L2 is incident as
illustrated in FIG. 2A, the light is changed to
left-circularly-polarized light L1. The left-circularly-polarized
light L1 passing through the geometric phase lens 100 converges to
a focus f1 having a positive focal length X1. When
left-circularly-polarized light L1 is incident as illustrated in
FIG. 2B, the light is changed to right-circularly-polarized light
L2. The right-circularly-polarized light L2 passing through the
geometric phase lens 100 diverges along paths extending from a
focus f2 having a negative focal length X1. When linearly-polarized
light or non-polarized light L is incident as illustrated in FIG.
2C, the energy of the incident light is bisected, so that a portion
of the incident light is changed to left-circularly-polarized light
L1, which converges to a positive focus f1, while another portion
of the incident light is changed to right-circularly-polarized
light L2, which diverges along paths extending from a negative
focus f2.
[0057] Accordingly, incident light emitted or reflected from the
target object 10 is changed to left-circularly-polarized light and
right-circularly-polarized light through the geometric phase lens
100, so that an interference pattern is formed by mutual
interference between the left-circularly-polarized light and
right-circularly-polarized light. The interference pattern is
formed on the image sensor 200 to be obtained by the image sensor
200.
[0058] The self-interference holographic system according to the
present disclosure can obtain information regarding incident light,
on the basis of information regarding the interference pattern
obtained by the image sensor 200. That is, a holographic image can
be obtained using the interference pattern obtained by the image
sensor 200.
[0059] The holographic image obtained as above can be displayed on
a hologram display device, which may be used in a variety of
forms.
[0060] As described in the Background section, in the case of a
holography technique, both light source information and twin-image
information of an object are recorded in the image sensor 200
obtaining the holographic image using the interference pattern, so
noise may be created. Accordingly, a phase shifter 500 is provided
to remove the light source information and the twin-image
information from the holographic image.
[0061] The phase shifter 500 according an exemplary embodiment is
disposed in front of the geometric phase lens 100 and is configured
to change the phase of light entering the geometric phase lens 100.
The phase shifter 500 is configured based on geometric phase
shifting in which a phase is shifted while an optical path is
maintained, instead of dynamic phase shifting in which an optical
path is directly changed, unlike in the related art.
[0062] Since the phase shifter 500 is configured based on geometric
phase shifting, the phase shifter 500 having a simple structure may
be fabricated. Since the phase shifter 500 is independent of phase
shifting based on a change in the optical path, it is possible to
obtain phase-shifting effects having fewer errors in all wavelength
ranges.
[0063] The phase of incident light is sequentially shifted through
the phase shifter 500. The phase-changed light is then changed to
left-circularly-polarized light and right-circularly-polarized
light while passing through the geometric phase lens 100. The
left-circularly-polarized light and the right-circularly-polarized
light form interference patterns. The image sensor 200 can
sequentially obtain interference patterns formed by the interaction
between the left-circularly-polarized light and the
right-circularly-polarized light, produced from the incident light
that has been sequentially phase-changed, and produce a single
birefringence holographic image by combining and computing the
interference patterns.
[0064] The self-interference digital holographic system having the
above-described configuration, according to an exemplary
embodiment, can obtain interference patterns of incident light
using the geometric phase lens, which is a simple optical
component, and obtain a holographic image using the interference
patterns. Since the self-interference digital holographic system
can be simply fabricated in a low cost and in a miniaturized size,
the use thereof can be extended to a wide range of
applications.
[0065] In addition, since the phase of incident light can be
changed by rotating the polarizer, which is a simple optical
component, without the use of complicated optical equipment or the
like, an economically inexpensive and complete transmission system
can be provided. In addition, the phase change can be performed by
geometric phase shifting through the rotation of the polarizer, as
will be described later, instead of dynamic phase shifting in which
an optical path is directly changed. Since phase shifting is
independent of a change in the optical path, it is possible to
obtain phase-shifting effects having fewer errors in all wavelength
ranges. Accordingly, a more accurate holographic image can be
produced.
[0066] An incident lens 300 may be disposed in front of the phase
shifter 500. The incident lens 300 condenses incident light
propagating from the target object 10, allowing the incident light
to enter the geometric phase lens 100 through the phase shifter
500. The incident lens 300 is designed to introduce a portion of
light, propagating from the target object 10 in random directions,
to the holographic system according to the present disclosure, and
functions as an object lens of a camera, a microscope, or the
like.
[0067] FIGS. 4 to 6 are perspective views illustrating a variety of
configurations of the self-interference digital holographic system
according to an exemplary embodiment.
[0068] The phase shifter 500 according to an exemplary embodiment
is configured based on geometric phase shifting instead of dynamic
phase shifting in which an optical path is directly changed. As
illustrated in FIGS. 4 to 6, the phase shifter 500 may include a
turntable-shaped rotatable polarizer 510 and a polarizer driver 520
rotating the rotatable polarizer 510.
[0069] The rotatable polarizer 510 is a polarizer by which the
incident light is changed to linearly-polarized light. The
rotatable polarizer 510 is disposed in front of and concentrically
with the geometric phase lens 100 such that the incident light
enters the geometric phase lens 100 through the rotatable polarizer
510, and is configured to change the incident light to
linearly-polarized light.
[0070] The polarizer driver 520 is configured to rotate the
rotatable polarizer 510 about the central axis, as indicated by
arrows in FIGS. 4 to 6. The polarizer driver 520 may include a
pressing roller (not shown) rotating in close contact with the
periphery of the rotatable polarizer 510, a drive motor (not shown)
rotating the pressing roller, and the like. The polarizer driver
520 may have a variety of other structures that can rotate the
turntable-shaped rotatable polarizer 510.
[0071] The polarizer driver 520 may be configured to sequentially
rotate the rotatable polarizer 510 by an angle of 45.degree..
[0072] It is possible to sequentially obtain interference patterns
formed by the interaction between the left-circularly-polarized
light and the right-circularly-polarized light, produced from four
beams of the incident light that have been sequentially
phase-changed by the phase shifter 500, and produce a single
birefringence holographic image by combining and computing the
interference patterns.
[0073] In addition, as illustrated in FIGS. 4 to 6, a fixed
polarizer 600 may be provided between the geometric phase lens 100
and the image sensor 200 to change the left-circularly-polarized
light and the right-circularly-polarized light, changed by the
geometric phase lens 100, to linearly-polarized light while
allowing the left-circularly-polarized light and the
right-circularly-polarized light to pass therethrough.
[0074] Although interference patterns may be formed on the image
sensor 200 by the interaction between the left-circularly-polarized
light and the right-circularly-polarized light without the fixed
polarizer 600, it is possible to change the
left-circularly-polarized light and the right-circularly-polarized
light, changed by the geometric phase lens 100, to the same
linearly-polarized light using the fixed polarizer 600, thereby
further enhancing the interference between the
left-circularly-polarized light and the right-circularly-polarized
light and producing clearer interference patterns on the image
sensor 200.
[0075] In addition, as illustrated in FIG. 5, the incident lens 300
may be disposed in front of and concentrically with the phase
shifter 500, allowing the incident light propagating from the
target object 10 to enter the geometric phase lens through the
phase shifter 500. The incident lens 300 is designed to introduce a
portion of light, propagating from the target object 10 in random
directions, to the holographic system according to the present
disclosure, and functions as an object lens of a camera, a
microscope, or the like. The incident lens 300 may not be provided,
in which case the geometric phase lens 100 may further function as
an object lens.
[0076] In addition, as illustrated in FIG. 6, a floating lens 400
may be disposed between the geometric phase lens 100 and the fixed
polarizer 600, allowing the left-circularly-polarized light and the
right-circularly-polarized light, changed by the geometric phase
lens 100, to pass therethrough, thereby extending the optical paths
of the left-circularly-polarized light and the
right-circularly-polarized light. The floating lens 400 may be
selectively disposed by a user, depending on the configuration of
the holographic system. For example, in the case of a microscope, a
telescope, or the like, the floating lens 400 may be used to extent
the optical paths. In addition, since the floating lens 400 extends
the optical paths of the left-circularly-polarized light and the
right-circularly-polarized light, the effect of interference
between the left-circularly-polarized light and the
right-circularly-polarized light can be further enhanced and
clearer interference patterns can be obtained.
[0077] FIG. 7 is a conceptual view illustrating a configuration of
a self-interference digital holographic system to which a space
division phase shifter according to another exemplary embodiment is
applied; and FIG. 8 is a perspective view illustrating a specific
configuration of the self-interference digital holographic system
according to another embodiment.
[0078] The self-interference digital holographic system according
to another exemplary embodiment further includes a space division
phase shifter 700 changing the left-circularly-polarized light and
the right-circularly-polarized light, changed by the geometric
phase lens 100, to linearly-polarized light to enter the image
sensor 200.
[0079] Described of the principle of the self-interference digital
holographic system without the space division phase shifter 700,
incident light is changed to left-circularly-polarized light and
right-circularly-polarized light while passing through the
geometric phase lens 100 and interference patterns are formed by
the interference of the left-circularly-polarized light and the
right-circularly-polarized light, as described above. The
interference patterns are formed on the image sensor 200 to be
obtained by the image sensor 200.
[0080] In the case of a holograph technique, both light source
information and twin-image information of an object are recorded in
the image sensor 200 obtaining a holographic image using an
interference pattern, so noise may be created. Accordingly, a phase
shift module is provided to remove the light source information and
the twin-image information from the holographic image. However,
there is a fundamental problem, in that none of generally studied
phase shift modules can capture a moving image of a moving object,
since such phase shift modules are configured to change the phase
of light in a time sequence.
[0081] According to another exemplary embodiment, the space
division phase shifter 700 based on space division is provided as a
phase shifter.
[0082] The space division phase shifter 700 is disposed in front of
the image sensor 200, and causes the left-circularly-polarized
light and the right-circularly-polarized light, changed by the
geometric phase lens 100, to be changed to two beams of
linearly-polarized light before entering the image sensor 200.
Here, the space division phase shifter 700 is configured such that
the linearly-polarized light beams entering the image sensor 200
have different phases according to a plurality of divided sections
of a light receiving area of the image sensor 200.
[0083] Described in more detail, the space division phase shifter
700 may include a micro-polarizer array 710 attached to the front
surface of the image sensor 200. The micro-polarizer array 710 is
comprised of a plurality of micro-polarizers 711 changing
transmission light to linearly-polarized light, the plurality of
micro-polarizers 711 being arranged to correspond to the plurality
of divided sections of the image sensor 200.
[0084] For example, in the case in which the image sensor 200
includes a plurality of pixels, the plurality of divided sections
of the image sensor 200 may be divided according to the plurality
of pixels, respectively, and the plurality of micro-polarizers 711
may be configured to correspond to the plurality of pixels of the
image sensor 200, respectively. Accordingly, the plurality of
micro-polarizers 711, attached to the front surface of the image
sensor 200, may be in the same arrangement as that of the pixels of
the image sensor 200.
[0085] Each of the plurality of micro-polarizers 711 is provided as
a polarizer changing transmission light to linearly-polarized
light. Here, light transmission axes a1, a2, a3, and a4 of the
plurality of micro-polarizers 711 have different angles, such that
linearly-polarized beams, changed by the micro-polarizers 711, have
different phases according to the micro-polarizers 711.
[0086] For example, each of the light transmission axes a1, a2, a3,
and a4 of the micro-polarizers 711 may be configured to have any
one of four (4) different types of light transmission axis angles,
which sequentially vary by 45.degree., as illustrated in FIG. 8.
According to this configuration, linearly-polarized light changed
by each of the micro-polarizers 711 has a phase difference of
45.degree., depending on the angle of the light transmission axes
a1, a2, a3, and a4. The plurality of micro-polarizers 711 having
different types of light transmission axis angles may be provided
such that the same number of micro-polarizers 711 are provided for
each type of light transmission axis angle.
[0087] According to this configuration, incident light propagating
from the target object 10 is changed to left-circularly-polarized
light and right-circularly-polarized light while passing through
the geometric phase lens 100. The left-circularly-polarized light
and the right-circularly-polarized light are changed to two
linearly-polarized beams while passing through the micro-polarizers
711 arranged to correspond to the divided sections of the image
sensor 200, before entering the image sensor 200. Then, the
linearly-polarized beams are received by the image sensor 200.
Here, the interference of two linearly-polarized beams, changed
from left-circularly-polarized light and the
right-circularly-polarized light, forms an interference pattern to
be obtained by the image sensor 200. Such an interference pattern,
formed from the two linearly-polarized beams, is formed by each of
the plurality of micro-polarizers 711. The micro-polarizers 711
have different phases of linearly-polarized light due to different
angles of the light transmission axes a1, a2, a3, and a4.
Accordingly, it is possible to simultaneously obtain interference
patterns formed from four phase-shifted linearly-polarized
beams.
[0088] In other words, in the process of obtaining a holographic
image using interference patterns, a plurality of interference
patterns having different phases are obtained using the phase
shifter in order to remove noise. The phase shifter according to
exemplary embodiments can simultaneously obtain a plurality of
phase-changed interference patterns by space division, although
phase shifters of the related art are configured to change the
phase in the time sequence.
[0089] As described above, it is possible to simultaneously form
interference patterns from a plurality of phase-shifted
linearly-polarized beams and combine and compute the obtained
interference patterns, thereby obtaining a single birefringence
hologram.
[0090] Accordingly, the self-interference digital holographic
system according to exemplary embodiments can obtain a single
birefringence hologram by a one-time image-capturing process by
simultaneously forming interference patterns from phase-shifted
linearly-polarized beams by space division, instead of sequentially
obtaining the interference patterns. In addition, since a plurality
of interference patterns can be simultaneously obtained by a
one-time image-capturing process, it is possible to capture a
holographic image of an object moving over time, such as a living
thing, as well as an image of a still object. Accordingly, it is
possible to capture moving holographic images.
[0091] In addition, it is possible to obtain interference patterns
of incident light using the geometric phase lens, which is a simple
optical component, and obtain a holographic image using the
interference patterns. Since the self-interference digital
holographic system according to exemplary embodiments can be simply
fabricated in a low cost and in a miniaturized size, the use
thereof can be extended to a wide range of applications.
[0092] In addition, the fixed polarizer 600 may be provided in
front of the geometric phase lens 100 such that incident light
enters the geometric phase lens 100 through the fixed polarizer
600. The fixed polarizer 600 changes the incident light to
linearly-polarized light.
[0093] Although a plurality of phase-shifted interference patterns
may be obtained as described above, without the fixed polarizer
600, incident light can be changed to linearly-polarized light by
the fixed polarizer 600 before entering the geometric phase lens
100 in order to further enhance the interference of
left-circularly-polarized light and right-circularly-polarized
light, as well as the interference of the linearly-polarized light
enabled by the space division phase shifter 700. Consequently,
clearer interference patterns may be formed on the image sensor
200.
[0094] In addition, the incident lens 300 may be provided in front
of the fixed polarizer 600 to converge incident light propagating
from the target object 10, so that the incident light enters the
geometric phase lens 100 through the fixed polarizer 600.
[0095] The incident lens 300 may be disposed in front of and
concentrically with the fixed polarizer 600. Accordingly, the
incident light propagating from the target object 10 to enter the
geometric phase lens 100 through the fixed polarizer 600. The
incident lens 300 is designed to introduce a portion of light,
propagating from the target object 10 in random directions, to the
holographic system according to the present disclosure, and
functions as an object lens of a camera, a microscope, or the
like.
[0096] In addition, the floating lens 400 may be disposed between
the geometric phase lens 100 and the space division phase shifter
700, allowing left-circularly-polarized light and
right-circularly-polarized light, changed by the geometric phase
lens 100, to pass therethrough, thereby extending optical paths of
the left-circularly-polarized light and the
right-circularly-polarized light. The floating lens 400 may be
selectively disposed by a user, depending on the configuration of
the holographic system. For example, in the case of a microscope, a
telescope, or the like, the floating lens 400 may be used to extent
the optical paths. In addition, since the floating lens 400 extends
the optical paths of the left-circularly-polarized light and the
right-circularly-polarized light, the effect of interference
between the left-circularly-polarized light and the
right-circularly-polarized light can be further enhanced and
clearer interference patterns can be obtained.
[0097] The foregoing descriptions of specific exemplary embodiments
of the present disclosure have been presented with respect to the
drawings and are not intended to be exhaustive or to limit the
present disclosure to the precise forms disclosed, and obviously
many modifications and variations are possible for a person having
ordinary skill in the art in light of the above teachings. It is
intended therefore that the scope of the present disclosure not be
limited to the foregoing embodiments, but be defined by the Claims
appended hereto and their equivalents.
* * * * *